沉管隧道基槽边坡振动台试验及动力特性

Shaking Table Test on Seismic Characteristics of Trench Slope of Immersed Tunnel

为研究沉管隧道基槽边坡的动力特性,以在建的港珠澳大桥沉管隧道工程为背景,设计并完成了几何比尺1∶60的沉管隧道基槽变坡度边坡大型振动台模型试验,并对试验模型的动力特性进行了分析。针对试验设计的细节尤其是相似关系设计和模型土设计进行了重点介绍。基于Buckingham-π相似原理,通过量纲分析的方法得到了相似关系控制方程,并以此方程为基础推导得到了试验所需各物理量的动力相似关系;利用锯末和砂按照一定比例混合配制模型土,通过一系列室内动三轴试验研究了模型土与原状土动力的特性,找到了动力特性与原状土相匹配的模型土;根据实际工程的场地状况和振动台试验设备的要求,设计并制作了长、宽、高分别为4.5,4.0,1.2m的刚性模型箱。通过振动台试验研究了输入不同频谱、峰值加速度和频率相似比地震波的变坡度场地地震响应差异,探讨了边坡的动力响应规律。试验验证了模型箱边界效应,边界处土体的加速度响应与中间处土体基本一致,并与其他试验结果进行了对比。结果表明:土体对输入的地震波具有明显的放大作用;不同频谱地震波作用下,边坡坡面的加速度响应具有明显的差异;不同地震动峰值加速度输入条件下,峰值加速度(PGA)放大系数沿坡面分布规律基本一致;不同频率的地震波作用下,变坡度PGA放大系数随频率相似比的增大而增大。

In order to investigate the seismic characteristics of trench slope of immersed tunnel,large-scale shaking table tests were designed and conducted on immersed tunnel trench slope model with the geometric scale of 1∶60on basis of the under-construction immersed tunnel engineering of the Hong Kong-Zhuhai-Macao Bridge,and the seismic characteristics of test modelwere analyzed.Details of experimental setup were first presented with particular focuses on design of the similitude relation and the model soil.Based on Buckingham-πtheory,governing equation of similitude relation was deduced using dimensional analysis,and other similitude relations of physical parameters needed in this test were obtained on basis of the governing equation.Model soil was prepared using a certain amount of sawdust and sand,and a series of laboratory dynamic tri-axial tests was carried out to investigate model soil and field soil.The model soil matching with field soil in terms of seismic characteristics was found.Rigid model box was designed and manufactured with length of 4.5 m,width of 4 mand height of 1.2 m.The differences of seismic response of gradient-changing slops under seismic waves with different spectra,peak accelerations and frequency similitude ratios were investigated through shaking table tests and dynamic response of the gradient-changing slope was discussed.Boundary effect of model box was verified,and acceleration response at boundary was close to that at center,which was further compared with other test results.The results show that soil shows significant amplification impact on the input seismic wave.Acceleration response of the slop surface shows obvious difference excited by different sorts of seismic waves,but the amplification factor distribution trends of peak ground acceleration（PGA）are nearly the same in test cases of different peak acceleration inputs.The amplification factor of PGAfor gradient-changing slops increases with the increase of the frequency similitude ratio under seismic wave with different frequencies.